The gray, short-tailed opossum, Monodelphis domestica (also known as the "laboratory opossum"), is the predominant laboratory-bred research marsupial in the world and is used in investigations that span a broad range of topics relevant to human development, physiology, and disease susceptibility. In the past three years, excellent progress has been made In establishing a genomic resource base that is enabling new avenues of inquiry with this species in the areas of comparative genomics, gene and genome structure, and the detection and mapping of genes that influence developmental and physiologic phenotypes. Such resources include: a fully arrayed, publicly available bacterial artificial chromosome (BAG) library;an expanding linkage map;and a soon-to-be-completed full-genome sequence. In contrast, tools for modern functional genomic analysis (gene regulation and expression) are sorely lacking for this and all other marsupial species. Given the diversity of basic biological and health-related research currently being conducted with M. domestica, there is a critical need for tools that can be used for investigating variation in gene expression in normal and abnormal physiologic and developmental states, and in animals that exhibit varying susceptibilities to disease conditions and developmental anomalies. The fundamental objective of the studies proposed in this application is the construction of a broadly representative series of expressed sequence (cDNA) libraries and corresponding high-density gene expression arrays that can be utilized for gene expression profiling in a diversity of basic and biomedically oriented research applications using M. domestica and other marsupial species. The proposed research will also establish an expressed sequence tag (EST) database and use this database for the construction of an expressed sequence map of M. domestica that will reveal differences in organization and gene content between the genomes of marsupial and eutherian mammals, particularly the human genome. An explicit objective of the proposed study is to make these cDNA libraries, gene arrays, and database resources fully accessible to the research community.